A model of the electrons in a metal or a plasma in
which they are regarded as forming a gas that interacts
with a uniformly distributed background of positive
charge to ensure that the system is electrically neutral.
It is analyzed theoretically using either classical
or quantum statistical mechanics and the kinetic theory
The electron-gas model accounts for many
properties of metals and plasma in a qualitative and
approximately quantitative way but cannot give an
accurate quantitative account of these systems, as
this would require the motions of the positive ions
to be taken into account.